Three tropical soils from Ghana, West Africa, were investigated in the laboratory for their potential as liners for waste containment. The key characteristic evaluated was the impact of municipal solid waste landfill leachate on the geotechnical, mineralogical, sorptive and diffusive properties and hydraulic conductivity of the soils. The observed unique characteristics of the soils included their silica: sesquioxide ratios that allowed them to be classified as either lateritic (ratio of 1.33–2.0) or nonlateritic (ratio greater than 2.0). After 5–11 pore volumes of leachate permeation through the soils, the specific surface of each soil decreased due to mineralogical transformations, while the cation exchange capacity of the soils increased. Na+ and K+ present at the exchange sites of the soils increased at the expense of desorbed Ca2+ . The effective diffusion coefficient, De , obtained for potassium was 1.3–2.0× 10−10 m2 ∕s while that of sodium was 7.3–14× 10−10 m2 ∕s . New minerals formed in the soils ...

Interactions between Three Tropical Soils and Municipal Solid Waste Landfill Leachate

Long term competent performance of liner systems is a critical issue in the design and construction of waste repositories due to adverse interactions associated with leachate generated by wastes. This study was conducted to verify the efficacy of fly ash stabilization in enhancing compatibility between lateritic soil and municipal waste leachate. Applications investigated include soil mixtures containing 0, 5, 10, 15, and 20% fly ash compacted at approximately 2% wet of optimum moisture content with modified proctor energy. Baseline hydraulic conductivity was first established at every level of fly ash content by permeating soil mixtures with tap water before permeation with leachate in a compaction mould permeameter using the falling head test method. Results show that the trend in hydraulic conductivity of specimen containing 0% fly ash was characterized by a gradual but erratic decrease which may suggests partial entry of the leachate cations into the double layer. Conversely, specimens containing fly ash showed a general trend consisting of an initial drop in k (up to an order of magnitude) that was followed by slight decrease sustained until k stabilized and later terminated. Above 10% fly ash content, the relatively high values of k observed was not connected with the reactivity of the soil mixtures with leachate, rather it may be attributed to excessive fly ash content that altered their textural and hydraulic properties. The result of this study is potentially significant in the assessment of fly ash as a compatibility enhancing agent which can be admixed in barrier materials that are susceptible to adverse reactions with the liquid to be contained.

Hydraulic Conductivity Tests for Evaluating Compatibility of Lateritic Soil—Fly Ash Mixtures with Municipal Waste Leachate

This paper highlights resource recovery and stabilization as the novel approach adopted in the rehabilitation strategy of the abandoned copper mine site (CMC mine) located in Northern Cyprus, recognized as a source of chronic pollution problems. The site holds 9.5 million tons of tailings stored in poorly equipped ponds. The waste contains pyrite and chalcopyrite undergoing slow oxidation; this way, sulfide has been partly converted to sulfuric acid causing severe acid mine drainage problems. The rehabilitation strategy adopted the EU’s key principle of resource recovery, where all tailings would be processed for copper recovery and stabilized to further prevent the chemical mobility of heavy metals before final landfilling. A leaching-cementation process, with no chemical usage, except for lime stabilization after recovery, was designed for this purpose. The corresponding action plan entailed that all the waste material be processed in situ, in a zero waste environment. Accordingly, the remediation will be carried out in a sequential process involving emptying the ponds for resource recovery, preparing the necessary number of emptied ponds with sufficient holding capacity, as selected landfill sites in a way to secure and provide all necessary measures imposed by international regulations for containing and controlling hazardous wastes. Finally closure plans will be implemented for the rehabilitation of the mining site to reclaim full attributes of natural characteristics.

Resource recovery as a sustainable perspective for the remediation of mining wastes: rehabilitation of the CMC mining waste site in Northern Cyprus

The acidification of paddy fields was studied in Guizhou Province, China. Affected by acid mine drainage, the pH value of irrigation water was 2.9 with the concentrations of iron and aluminium above 40 mg/L. Based on the pH(H2O) of topsoil, the paddy fields studied were classified spatially into three zones, the natural zone (pH value from 6.2 to 5.5), the acidified zone (pH value from 5.5 to 4.5), and the seriously acidified zone (pH value from 4.5 to 3.2), respectively. Comparing to the natural zone, the buffering processes for acidification of paddy soil were discussed by considering the changes of calcium, magnesium, potassium and aluminium in soils. The Ca, Mg and K were leached from the soil by the decomposition of carbonate and kaolinite. The leaching of Mg became less with the enrichment of iron in topsoil layer. When the soil pH was below 5.0, aluminium was leached from soil because of the dissolution of alumino silicate minerals. In addition, the hydrolysis of iron and aluminium in soil provided more protons to promote the soil acidification. Furthermore, the buffer capacity of paddy soil was discussed by the results of buffer experiment, based on which the pH buffer curve was drawn and the empirical formula for calculating the acidification rate was developed. Because pH buffer capacity of soil is about 2.78 cmolc/kg pH for the pH(H2O) value above 5.0, it is estimated that only another 50 years are needed for the pH(H2O) of the paddy soil decrease to 3.5 in the acidified zone if the acid water is used for irrigation continuously.

The study of soil acidification of paddy field influenced by acid mine drainage

In developing countries groundwater is used for drinking and other beneficial purposes. However, its purity and quality is compromised because of the way waste is disposed. Laboratory tests were carried out to evaluate the hydraulic conductivity of three reddish brown tropical soils (labeled MP1-MP3) compacted at −2, 0, 2 and 4% of optimum moisture content using four compactive energy levels namely Reduced Proctor (RP), Standard Proctor (SP), West African Standard (WAS) and Modified Proctor (MP) and then permeated in compaction mould permeameter under falling head condition. Hydraulic conductivity values approached 1 × 10−7 cm/s at optimum molding water contents and up to 4% wet of optimum. This was achieved when the dry unit weight was greater or equal to 6.10 kN/m2 at initial degree of saturation of 84% and compactive effort which should not be lower than SP. The results obtained compare favorably well with existing literature database for hydraulic structures, thus showing the suitability of the material for waste containment application.

Hydraulic conductivity of three compacted reddish brown tropical soils

The chemical and mineralogical compositions of three tropical soils, before and after permeation with 19–24 pore volumes of acid mine drainage (AMD), were assessed using X-ray diffraction and chemical analyses, in order to consider their potential value as clay liners. After permeation the CEC of one soil (Soil K) was reduced, partly due to structural modification of smectite by AMD. Conversely, the other soils (Soils A and H) showed increased CEC values due to structural changes in mixed layer vermiculite minerals, resulting in the formation of vermiculite as a separate phase in the soils. The specific surfaces of the soils were reduced. AMD caused changes in the variable charge properties of the soils due to the composite effects of soil pH and organic matter reduction and the changes in composition of exchangeable ions. Dolomite, gibbsite, diaspore, magnesioferrite and hydroxy apatite were dissolved from the soils. Chlorite was mildly altered but kaolinite was structurally resistant to AMD attack. Jarosites were, however, formed in all the soils. It was concluded that the tropical soils studied could be effective sinks for zinc and nickel from AMD, but that Soils A and H would be the most desirable clay liners for acid mine waste containment due to their low hydraulic conductivity, high sorptive capacity and compatibility with AMD.

Chemical and mineralogical transformations in three tropical soils due to permeation with acid mine drainage

The interactions between acid mine drainage (AMD) and three tropical clayey soils have been studied through hydraulic conductivity and batch sorption/dissolution testing. After 19–24 pore volumes of AMD flow through the soils, the measured final hydraulic conductivity ranged between 1.1× 10−11 and 3.3× 10−11 m∕s . The pH, electrical conductivity, and solute breakthrough curves obtained suggested the soils had low acid-buffering capacities. Also, several chemical species were released from the soils due to AMD attack of soil grains and mineral. The batch tests revealed high dissolution of species such as sodium, cobalt, and sulfate from the soils by AMD. The results also indicated dissolution of metals from soil constituents, desorption of chemical species, and transformation and dissolution of soil minerals due to AMD attack. The results of the study showed that, in general, the soils were not effective in attenuating contaminants present in the AMD. Thus, they may not be used alone to construct liners fo...

Eric M. Frempong

Papers

Chemical and mineralogical transformations in three tropical soils due to permeation with acid mine drainage

Tropical Soils-Acid Mine Drainage Interactions: Breakthrough Curves and Some Transport Parameters

Geoenvironmental Assessment of Two Tropical Clayey Soils for use as Engineered Liner Materials